With the advent of DVDs and widescreen movie
presentation, everyone seems to want to have a BIG picture. And, I don't
mean just getting a 40" direct view. I am talking about 50", 60", and
larger.

Flat panel plasma screens are available in 63", and
probably by the end of 2004, maybe even 72" or 80". However, such plasmas
are really expensive, upwards of $20,000. That is beyond the average
consumer's budget.

Enter the front projector. A few years ago, when you
wanted to consider a front projector, you were talking about a huge box with
9" CRTs. It gave a great image, nice and big, beautiful color. But, again,
it was mucho dollars.

Digital projectors changed all that. The recent
Sanyo Z2
review is a good example. For $2,000 you can put the projector on your
coffee table and project it as big as you want. Let's say 72" wide. That
ought to do it for most family rooms wouldn't you say? Or 60", or 120".
Whatever you want. Just use the zoom lens.

And if you have not considered a front projector yet,
well, consider it now, because, wow, what a difference a big picture makes
when you have a big surround sound system.

OK, you might buy one, you say. But what about the
screen? Where will you put it? If you get a big projection screen, it will
block the speakers.

ClearPix

Several manufacturers make projection screens designed
specifically to solve the problem of wanting a screen so large that it gets
in the way of the speakers, namely, they are transparent to audio. They
accomplish by using perforations in the screen. A problem sometimes occurs,
however, with Moiré patterns being visible when watching movies. Comb
filtering can also occur in the audio high frequencies with perforations.

Screen Research, a French company, has introduced a new
product called ClearPix, which uses a material that apparently may have
originated in the French fashion industry.

ClearPix screens come in all sizes and shapes (4:3,
16:9, and 2.35:1), but only in two gains: 0.95 white and 0.75 gray. The
engineers at Screen Research decided to go with 0.95 gain instead of 1 or
higher because they wanted the screen to be a uniform white with no
hot-spotting. Today's digital projectors have higher brightness and better
contrast than a few years ago, and since the material is very expensive,
they decided to enter the market with a screen ideally suited to 3-chip DLP
projectors.

The fabric is a woven fiberglass material, coated with vinyl. Here is a
photo of the projection side of the screen, at a magnification that appears
(on my monitor anyway) about what it actually looks like if you are viewing
it from a normal computer monitor distance.

You can see the diagonal weave clearly. It is cut on the
bias (diagonal) so that it can be hung without curling at the edges.

There is a small amount of space between the fibers, and
this allows the sound to get through.

Now, because of the transparency, some of the light gets
through as well, specifically about 10%. Most of us don't have black walls
behind the screen, so this 10% can reflect off of the walls, not to mention
other objects behind the screen if you use the motorized version. (If you
mount the screen on the wall, the scrim is not necessary because you can
simply paint the wall behind the screen flat black.)

To remedy this, ClearPix also supplies a black scrim
material that can be ordered with the screen, and rolls down behind
the screen on a weighted baton when it is lowered. Here is a photo of the scrim material.

The projection screen material currently is called CP-2. Sometime
during the next year, CP-3 will be available, which is a lighter material
that is easier to put into fixed frames, and should also be less expensive.

The Tests

I did not have a full sized screen for review, but the StJohn Group kindly sent me two samples, each about 1 meter square. One
sample was the 0.95 white and the other was the black scrim.

Image-wise, the ClearPix was just a bit brighter than my
reference Stewart Grayhawk screen (non-perforated). Like the Grayhawk, the ClearPix had
essentially no falloff at side viewing angles, and no hot spots. But, the
most important thing was, I could see no Moiré patterns.

At normal viewing distances, I could not see any weave
pattern in the ClearPix, but up close, I could see it. Also, the pixels were
diffused a little bit, compared to the smooth surface of the Grayhawk. This
was expected, since the ClearPix surface is made up of tiny ridges due to
individual vinyl fibers. This does not necessarily translate to any
difference in resolution though.

I then tested the audio transparency.

For the test, I used a
Thiel CS2.4 speaker. I did not want to filter the results using MLS
techniques, so I placed a calibrated microphone just 3" from the Tweeter/Mid
driver. I then used pink noise and collected a simple SPL response, with the
total power set to 100 dB. After I collected the first response, with no
screen material, I placed the ClearPix 0.95 white screen over the front of
the speaker, equidistant in between the tweeter and the microphone, for the second
response test, followed by a third
response with both the screen and the black scrim.

Here are the results:

The red curve is with no screen material, blue is with
just the white screen, and yellow is with both the screen and the black
scrim. You can see that the curves are very close together. They are not
flat curves because I had the microphone very close to the tweeter/mid
driver and it was still picking up sounds from the woofer, which was farther
away. But, what I was interested in here was how the curves changed with the
screen.

The only noticeable differences were in the frequencies
at 5 kHz and above. For example, at 5 kHz, you can see the red on top, the
blue in the middle, and the yellow at the bottom, indicating several dB loss
at that frequency. At about 14 kHz, however, the blue is on top, meaning
that there was an increased response at that frequency with the screen. I
think these variations are just due to having the sound filtered through a
smaller number of fibers when the microphone was so close, and I suspect
they would even out with the speakers being placed farther behind the screen
and larger listening distances.

The main thing is that the response is still good even
with the screen and black scrim in front of the speaker. ClearPix
seems to be wonderful stuff!

Overall, there was about 1.5 dB loss of total audio power
through the screen and black scrim, which is what Screen Research states in their
specifications.

Conclusions

I was pleasantly surprised at how well the ClearPix
worked when it was placed in front of a speaker. It performs as advertised.
If you are in the market for a top notch projection screen, and want to put
your speakers behind it, definitely contact Screen Research (the StJohn
Group in North America) and get the samples for yourself to try out. It is a great
product!